Flotation of siliceous impurities from mineral-bearing material



June 10, 1952 w. A. HODGES 2,599,530

FLoTATIoN 0F sILlcEous IMPURITIES FROM MINERAL-BEARING MATERIAL T7-ORNE Y June 10, 1952 W, A, HODGES 2,599,530

' FLOTATION OF SILICEOUS IMPURITIES FROM MINERALBEARING MATERIAL Filed May 23, 1946 2 SHEETS-SHEET 2` Patented June 10, 1952 FLOTATION OF SILICEOUS IMPURITIES FROM MINERAL-BEARING MATERIAL William Arthur Hodges, Plant City, Fla., assignor to Swift & Company, Chicago, Ill., a corporation of 'Illinois Application May 23, 1946, Serial No. 671,683

Claims. (Cl. 209-166) their ores of the size between about minus 28 and about plus `150 mesh by otation, one method heretofore practiced extensively has been to make a pulp of the finely divided phosphatebearing ore in a flotation machine and to agitate the mixture in the presence of a suitable negative-ion reagent and frothing material While bubbling air therethrough. The froth collecting at the top of the machine contains a greater proportion of phosphate minerals and around 3 to per cent of siliceous impurities. In this method the phosphate particles are rendered non-wettable by employing reagents which selectively coat the phosphate material. Such reagents are usually a fatty acid, an inert oil, such as fuel oil, and caustic soda or a mixture of soap and an inert oil.

Another method of concentrating phosphate minerals is of a reverse type, which employs a positive-ion reagent, together with suitable frothing material, to selectively render the siliceous gangue non-wettable and hence iloatable. The float is removed as tailing, or waste, while the greater proportion of the phosphatic concentrate remains in the nonfloated material. This process has .been little used because of the large amounts of reagents Iequired to make it workable.

A third method of separating phosphate from thesiliceous gangue results from combining the two steps outlined above. According to this According to the double flotation method heretofore practiced, the phosphatic concentrate, after the intermediate treatment with the mineral acid, is further conditioned for the cationic reagent treatment. Heretofore it has been the practice to vigorously agitate the rougher phosphatic concentrate with the mineral acid, then thoroughly wash, scrub, as by raking, and deslime the concentrate before the treatment thereof with the positive-ion reagent, such as the higher amines or their salts. The underlying reason for such a thorough cleaning operation has Ibeen thought to be productive of better results, since by thoroughly cleaning the silica particles by agitating vigorously with mineral acid, then thoroughly washing to remove all scum and dead reagents, it Was thought that the silicavvould thus be in a condition better to receive the effects of the cationic reagent, thus making it possible not only to increase the amounts of floated silica, but also to decrease the amounts of reagents required to iioat the maximum of silica. In the art of froth-flotation it is generally considered to be good practice to rid the material to be subjected to flotation of all slimes, scums, and other impurities, the presence of which reduces the amounts of iloated material and increases the amounts of reagents required to iioat the mineral. By silica is meant the siliceous impurities, or gangue, usually found accompanying phosphate minerals as they exist in the natural state.

method a dual process is employed, whereby the phosphates are iirst roughly concentrated as by flotation with a negativerion reagent to produce a product containing a substantial amount of silica, and the rougher phosphatic concentrate, after a suitable intermediate treatment, subjected to the action of a cationic reagent in the presence of proper cooperating agents to float from the rougher phosphatic concentrate the siliceous impurities contained therein. The intermediate treatment between the two concentrating operations of the double flotation process consists in agitating the rougher phosphatic concentrate, obtained from the rst otation step, with a mineral acid, such as sulfuric acid, and then removing the dead reagents. The acid deadens or removes the charge of the phosphates s0 that they can no longer oat, and most of the dead negative-ion reagents, such as-soap and fuel oil, rise to the surface and may be removed.

I have now discovered that the use of a mineral acid when employed in a proper manner has the additional function of activating the silica contained in the rougher concentrate so as to make it more receptive to the effects of the reagents used in the second concentrating operation, but pursuant to the procedure heretofore practiced the activation of the silica by the mineral acid is destroyed, and thus not all of the functions of the mineral acid are utilized. On the other hand, if the activating property imparted to the silica by the mineral acid is utilized, results far superior to any heretofore achieved in the double flotation process for the recovery of` phosphate minerals are obtained.

3 4 in the mixing of the phosphatic concentrate with Figure 1 is a diagrammatic side elevation, partly the mineral acid and in the subsequent vigorous in section, showing the equipment used in the washing operations, and that such treatment mixing of anionic reagents and phosphatic feed, produces results opposite to those desired. The the rst otation step, the washing operation,

activation ofY the silica by the mineral aciLSv and the second flotation step.l 1I. perhaps. destroyed by the abrasive n,and rubbing VFigure 2 is a pl'an view of the mechanism shown action of one silica particle with another. I have in Figure 1.

also found that, whereas heretofore better results Figure 3 is a detailed side elevation of the washing. equipment.

gilt? @sectional end elevation of the ing equipment, taken on line 4--4 of Fighave been secured by the use 9i aminesamltsmsucfh as octadecyl amine acetate as ,the batonio rec-- 16 agent, in my process equally good results are wash achieved by the use of either the free amines'or ure, I the salts thereof. e 5n s aplan View of a perforated plate In order to retain the activation imparted by forming apartof the washing equipment. the mineral acid to the silica andto predispose Relerring-to-the drawings, phosphatic feed the silica to the positive-ion reagent treatment; is introduced into the rst of a series of mixers I have found that it is essential that thegtreat; Il) by4 means of chute E. The negative-ion rement of the rougher phosphatic concentrate agents, such as a fatty acid, an inert oil, and withnthe mineral lacid and the subsequent decaustic are introduced therein by mega nsoil linionandwashirg Vbe carefully "cont" 20 le "I I i3", yfrfespec tively'. The?' ..In arryfmg 'out theinve'ritom itis 'impor an' ntsarjeintrodicedsepaiate stiffer in; which stir triemjxture of priesphaticfedahd iIihinamaiEriaiS.. After 'stirring of theprewithih ,re his the result mixture kis liilutelV with. Water iiitro 1" l1 at the Avoverflow .la and tulp' which is introducedfinto the lirs of ries fffitatioineeiijs 2g... The fiotatioiie is df, anvconventionaltvpa and ,inc lh dr et the flotation delle #are 0i a tvpeivh ee 1ilesffr0hedby mtansefairirtro into the cells the bottom thereof by means f. .inlets 2.1,. W ich. dnm'. With air 111.16.22: Bubbling air, thgrpugh'V the pulpjoritaind in' 11's 20 ,Sja fr'ithinao'f the phosphatic *miel al T 'th rises tothe top ofkthfe4 cells and .Iiee aryallf jdisihegedjnfto lailrrsenlhw the tailings, or 'waste material', are impelledpver s fout.` VIffthe agitation is. too vigorous, the ddd 'teefthmghnn 2 5 mid .the ,mixture atiivaticn 'crine Silica is greatly impaireu. Ai's'o, ci acid fand frcugierjpriospnatic "ccjricentrate, as a in the decantation step and in thew'ashirig Iand 50 sl ry, 'is vp''rop'elle'd lby lliurifi'p 29 through line 3Q scrubbing Qperatipns theze'ntrate. is nariii'it "upper vessel 32, which 'is bfefabiya as quiescent a state fas possible, while box.V Line Sllis provided with four, outlfets 33, th/,enuscum and deadreagents are ijeri 1 o ve d n so as to\'eff ec` t uniform 'distribution of the .,Reieritifmf thecharee impartedtothe silica s1' rv. 'verthelngth "f 'V-bxZ- Sufit bvtlieminerelect. prodiieessuqhaChange 11.1 in des alin l's ffrlled bviilrlp .29 and@ theisilioaasto brins. aegutrtainramifications ,39 tqefft .the .ricealv ,Cntatpi the the. .second concentrating, Operation. .which e.. ,d with ,the materiali@ @legden thetharsiimcause superior results. l,or example, while actofthefphosphati materialby the negacording to the `prior art, notation of the silica n 1eag'ents,lan df to active the silicaonofccur's in an acid medium,V according to my Droc- 60 tained .therei n. The vz niring actioninthe pump ess :good results are achieved on the alkaline side, and 2in line Eil, although sufficient tobring about a'pH of about 7.4 to 8 usually producing the best :onitatv between ac id and phosphatic material, results. Moreover, according to the prior method i.sfinsuf ieht to deactivate the charge on the the use of amine salts as cationic reagents gives S'la mpatd theretqby the mineral acid,

bettr lresults while', in accordance with my proc- 65 fglf, ai Suitable amount V,of phosphatic slurry ess, Ifr'nay use the free 'amines vand amine salts sicqumllled il) VjlOOX` 32, Sufcientwatenis interchangeably :as cationic reagents. Be'cause'of int? @$1.969 111130 ,.V-bOX, 3'2 by means of line 34 these.'r'nodications in the second 'concentrating l"0.. @lOll/the dead anionic` reagents Yand reoperation, it is rpossible to eiect a more. complete llnllg, rllllalcid, 'but insufficient 'to oversep'aration of the 'silica impurities from the 7o 119W, any Solid..n latter- The spent negative-fion rougher phosphatic concentrate, .whereby asilica ljegffnl'fsn the mineral 'acid are collected *in float freer of phosphates and a nal 'phosphatic liturrder` 31 andrernoved to waste through 'utconcentrat'e containing less silica are obtained. let 38. The.washing operation 'in V''box 32 re-l preferred embodiment o f the invention is v.moves roughly 15 per cent ofthe dead "reagents illustrated by the following drawings. and excess mineral acid.

ing boxes, or vessels, gives direction to the phosphatic material and makes possible a funneling of the material from one place to another with a minimum of agitation. As the phosphatic Inaterial enters the Washing tubs 45, it is met with a countercurrent of clean water introduced through inlets 4l` (Figure 4), the water coming up through the perforated plates 48, which are placed in the bottom of washing boxes 45. Plates 48 are provided with a large central opening 49 surrounded by a number of smaller openings. The velocity of `water entering the Wash boxes is sufficient to overovv remaining dead reagents, but insuicient to prevent the phosphatic material from settling and passing through the openings 48 of the perforated plates 48 and through outlets 50 into launder 5|.

. The phosphatic material flows into overflow 53, Where the positive-ion reagents for the flotation of silica are collectively introducedvby means of line 54, after which the material is frothed therewith in cells `'which are of the same type as those employed in the first concentrating operation, namely, cells 20. `Air is introduced into the cells by inlets 56`Whic`h connect with air line 51. Silica in the form of a froth results from the bubbling of air through the cells and is gathered in launder B0 and removed through line 6 I, while the depressed phosphatic material is collected at 62.

As hereinbefore mentioned, the mineral acid treatment of the rougher phosphatic concentrate not only serves to deaden the effects of the reagents employed to float the phosphates from phosphatic feed, but also activates the silica which remains in the rougher phosphatic concentrate after the rst concentrating operation,

and which it is desired to remove therefrom by a later flotation step employing reagents of a charge opposite to that possessed by the reagents used to oat the phosphates. These positive-ion reagents oat the silica and depress the phosphates. The power of the positive-ion reagents to float the silica is enhanced by thepreservation of the activation imparted to the silica by the mineral acid. This activation of the silica by the mineral acid is readily destroyed, and the means employed in mixing acid with the rougher phosphatic concentrate and in subsequently washing the resultant mixture are such as to effect mixing and Iwashing with a minimum of agitation, since too much agitation destroys the activation of the silica. `According to the invention herein described, the washing means are effective in washing the rougher phosphatic concentrate and also in preserving the activation of the silica. For best results, it is important that the Washing of the material in the V-box and in the washing tubs be carried out as promptly as possible, since the silica tends to become deactivated upon prolonged standing with the water in the V-box and wash tubs.

In order to illustrate how silica may be activated` by means of a mineral acid and subsequently deactivated by scrubbing, the following examples are given, in which the silica was in the form of minus 35 mesh sand that had been dil 6. washed clean of slimes and other impurities, and the mineral acid was sulfuric.

Example I 300 grams of Wet sand were treated 'with 0.5 g. of per cent sulfuric acid. The mixture of acid and sand in a pulp of about 50 per cent solids Was conditioned in a glass jar in which the sand was not allowed to come in contact with any metal. The acid water was then decanted, and the sand washed once with clean water. The treated sand was then introduced into a laboratory flotation cell with 0.5 g. of sodium hydroxide, 0.04 g. of amine reagent, and 0.04 g. of B-23 frother (a product marketed by DuPont consisting' of 40-45 per cent of 2-4 dimethylpentanol-l, 40-45 per cent 2-4 dimethylhexanol, and 8-10 per cent of unidentiiied ketones). In this test 209 g. of silica were floated.

Emample II 300 grams of wet sand were treated with 0.5 g. of 95 per cent sulfuric acid. The mixture of acid and sand in a pulp of about 50 per cent solids was conditioned in a glass jar in which the sand was not allowed to come in contact with any metal. The acid Water was then decanted, and the sand washed once with clean water. The sand was then scrubbed for ve minutes in a laboratory mixer and washed once with clean water. The treated sand Was then introduced into the laboratory M. S. cell With 0.5 g. sodium hydroxide and 0.4 g. of amine reagent and 0.04 g. of B-23 frother. In this test only 142 g. of silica were oated, as compared with Example I in which no scrubbing or agitation of the silica occurred as was the case here.

Example III 300 grams of wet sand were introduced into a laboratory M. S. cell with 0.05 g. of sodium hydroxide, 0.04 g. of an amine reagent containing 70 per cent primary amines and 30 per cent nitriles obtained from double distilled cottonseed fatty acids, and 0.04 g. of B-23 frother. In this test, wherein the acid treatment of sand was omitted, only 32 g. of silica were floated.

In addition to observing special conditions in the washing step, I have found that, in order to achieve best results, flotation of the silica in the second concentrating operation is carried out at an alkaline pH. Although a pI-I range of '7-8 produces satisfactory results, still better results are obtained at a pH of between 7.4 and 8. Adjustment of the pH is effected by means of any suitable base, such as the hydroxides of the alkali metals and of the alkaline earth metals. Sodium hydroxide is generally to be preferred for it is readily available and consequently cheap. The proper pH range serves to depress the phosphates, and I have found that this effect may be enhanced by the addition of starch to the sodium hydroxide solution.

Although sulfuric acid is the preferred mineral acid for the preconditioning of the concentrate prior to the treatment thereof in the second concentrating operation, other mineral acids, such as hydrochloric acid and nitric acid, may be employed. Other acid reacting substances, for example. acid reacting inorganic salts, such as sodium acid sulfate, potassium acid sulfate, etc., maybe employed. While the eifective amounts of these latter substances are large, it is not intended to exclude them from the scope of the invention and are embraced by the term mineral acid used in the claims.

As igtiveao reagents for the flotation of phosphates in the rst concentrating operation may be mentioned fatty acids of both animal and vegetable origin and their soaps, fatty acids obtained from wood by-products, the resin acids, their soaps, esters of inorganic acids with high nitileculai` weight aliphatic alcohols, etc.

Examples of positive-ion reagents for the fiotation f silica in the second concentrating operation are the high molecular weight aliphatic amines and their salts, the resin amines and their salts, esters formed between the high molecular weight fatty acids and amino alcohols, etc. In general, however, preference is for the high molecular weight vfree aliphatic amines, such as nfno'nohexadecyl, n-inonoctadodecyl, and ninonoqotadecemyl amines. y

Obviously, the amounts of flotation reagents in either concentrating step may be varied within wide limits. Good results may be achieved in floating the phosphates by using 0.3 to 1.0 pounds of ,per cent sodium hydroxide, 0.05 to 2 pounds of fatty acids, 1 to 4 pounds of fuel oil, all for each ton of feed.

In they second concentrating operation, approximately 0.04 pounds of distillate or kerosene, 0.14 to 0.16 pounds of positive-ion reagent, approximately ().04 pounds of frother, pine oil or the higher alcohols such as BJZS, plus 0.05 to 0.2 of 20 per cent 4sodium hydroxide, are sufficient ainounts of silica Aflotation reagents for each ton of original feed. The amount of sodium hydroxide indicated above is usually'sufoient to bring the pH of the pulp up to 7 .4 to 8.0.

It is, of course, understood by those skilled in 'the art that suitable cooperating agents other than those mentioned above may be employed as effectively. Also, it is to be understood that some of the substances mentioned may not only be Ysubstituted by others, but may be omitted altogether.

In order to further illustrate the practical operation of the invention, comparative test runs will now be described on two sample portions of the same phosphatic lfeed which had been screened over a 2'8 mesh screen. The fraction passing through the screen was washed and subjected to the 'first flotation step to float a rougher phosphate concentrate therefrom. Before flotation, a pulp ofabout per cent solids was made of the phos'ph'atic feed. In both samples the same amounts of negative-ion reagents were employed foreach ton of feed, namely, 0.3 pounds sodium hydroxide, 0.4 pounds fatty acid, 1.39 pounds fuel oil. Both samples of rougher phosphatic concen- Y trate 'were then mixed with 3.0 pounds of 95 per cent sulfuric acidperton of rougher concentrates. In -sample No. 1 the mineral acid and phosphatic material ywere thoroughly agitated, the dead reagents decanted, and the phosphates thoroughly rwashed with water and scrubbed by raking. Sample No. 2 was subjected to the mineral acid treatment and subsequent washing in accordance with Ythe Yprinciples of this invention; that is, the rougher phosphatic concentrate was mixed with the 'acid and washed with water with a minimum of agitation. After the mineral acid and subseduent washing operations, both samples of phosvp-hates were treated with positive-ion reagents to float the silica therefrom. vSample No. 2, treated in accordance with this invention, was mixed with v0.4 .pounds Isodium hydroxide, 0.32 'pounds of an amine reagent comprising a mixture vof the 8. amines' n-'monohexadecyL n-monooctadodecy1 and n-monooctadecemyl, the pI-'I of the resultant mixture being 7.5. The mixture was frothed and the silica floated. The amount of silica in the finished concentrate was 1.61 per cent. The rougher phosphatic concentrate of sample No. 1, which had been thoroughly cleaned and scrubbed following the mineral acid treatment, was formed into a pulp of about 25 per cent solids and frothed in the presence of about 0.32 pounds of octadecyl-'f amine acetate, the pH of the solution being 6.8. The amount of silica remaining in the finished concentrate in this case was 4.46 per cent.

In another comparative test wherein two sam-` ples were treated similarly, as above described, the amount of silica remaining in the finished concentrate treated in accordance with prior art methods was 7.86 per cent, whereas the silica content in the finished concentrate obtained by fol-V- lowing the principles of the invention was 2.02 per cent.

While the invention has been described as directed to the concentration of phosphate min'- erals from their ores, it is not to be intended 'as being limited to the purification of phosphates only. Other ores, such as those containing lead, zinc, iron, or copper minerals, or even coal, which are subjected to a frotheflotation process to r`e=- move the siliceou's impurities therefrom, fall within thescope of this invention. That is, the invention is applicable to all cases in the art of froth-flotation wherein the siliceous impurities are to be floated efiiciently, which effect may be achieved by activating the silica and maintaining Y it in an active state, as hereinabove described.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only 'such limitations should be imposed as are indicated 1in the appended claims.

I claim:

1. In the process of treating minerahbe'aring material by notation whereby the silice'ous im* purities incorporated therewith are oated, the steps of mixin'gmineral acid with said 'mineralbearing material to activate the siliceous impu'ri ties, Howing said mixture to a quiescent zone, contacting' said mixture with water diffused vinto 'said zone whereby substantially all of the acid is removed, witn'drawmg said minerai-bearing material from said Zone, and adding silica Aflotation reagents thereto before any appreciable agitation has destroyed the acid activation of the silica.

2. In the process of treating Vmineral-bearing material by flotation whereby the siliceous impurities incorporated therewith are iioa'tedl 'the steps of mixing mineral acid 'with said mineral-bearing material to activate the silio'eous impurities, nowing the mixture so formed to 'a 'quiescent zone, Washing said material with Water diffused into said zone to remove substantially all or 'said acid therefrom, withdrawing said washed, acid-treated, mineral-bearing material from said zone, adding positive-ion reagents "to said JI'n'a'teriahl before any appreciable agitation has destroyed Vthe acid activation of the silica, and o'ating the 'si'liceous impurities at a pH between 'about 7.4 'and 8.

3. The process 'of concentrating phosphate minerals from their ores, 'which comprises inakirig a pulp of the 'ore of `a size suitable for flotation, subjecting said pulp to a concentrating operation in the "presence of 'a negative-ion reagent to separate la rougher phosphatic concentrate said phosphatic concentrate with mineral acid to destroy the effects of the negative-ion reagents and to activate the silica, owing the mixture of concentrate and acid to a quiescent zone, washing the acid-treated concentrate with water diiused into said zone to remove the spent reagents and substantially all of the acid from said concentrate, and then subjecting the pulp of the phosphatic concentrate before any appreciable agitation has destroyed the acid activation of the silica to a second concentrating operation in the presence of a positive-ion reagent to separate therefrom a greater proportion of silica, thereby producing a relatively pure phosphatic concentrate.

4. The process of concentrating phosphate minerals from their ores, which comprises making a pulp of the ore of a size suitable for flotation, subjecting said pulp to a concentrating operation in the presence of a negative-ion reagent to separate a rougher phosphatic concentrate admixed with a lesser proportion of silica, mixing said phosphatic concentrate with mineral acid to destroy the effects of the negative-ion reagents and to activate the silica, Washing said concentrate with water diffused into a quiescent zone to remove the spent reagents and substantially all of the acid from said concentrate, removing said washed, acid-treated concentrate from said zone, and then subjecting the pulp of the phosphatic concentrate before any appreciable agitation has destroyed the acid activation of the silica to a second concentrating operation in the presence of a positive-ion reagent at a pH of about between 7.4 and 8 to separate therefrom a greater proportion of silica, thereby producing a relatively pure phosphatic concentrate.

5. In the process of treating mineral-bearing material by flotation whereby the siliceous impurities incorporated therewith are floated, the steps of mixing mineral acid with said mineralbearing material to activate the siliceous impurities, flowing the mixture thus formed to a quiescent settling zone, withdrawing the settled concentrate from the bottom oi said zone,4 introducing said concentrate into a quiescent Washing zone, diffusing Water into said zone to float substantially all of the acid from said concentrate, removing the settled, washed concentrate from the bottom of said zone, and adding positive-ion reagents to the settled, washed concentrate before any appreciable agitation has destroyed the acid activation of the silica.

*WILLIAM ARTHUR HODGES.

REFERENCES CITED The following reierences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,881,611 Hynes Oct. 11, 1932 2,267,496 Ellis Dec. 23, 1941 2,423,022 Herenhoif June 24, 1947 2,461,817 Greene Feb. 15, 1949 

1. IN THE PROCESS OF TREATING MINERAL-BEARING MATERIAL BY FLOTATION WHEREBY THE SILICEOUS IMPURITIES INCORPORATED THEREWITH ARE FLOATED, THE STEPS OF MIXING MINERAL ACID WITH SAID MINERALBEARING MATERIAL TO ACTIVATE THE SILICEOUS IMPURITIES, FLOWING SAID MIXTURE TO A QUIESCENT ZONE, CONTACTING SAID MIXTURE WITH WATER DIFFUSED INTO SAID ZONE WHEREBY SUBSTANTIALLY ALL OF THE ACID IS REMOVED, WITHDRAWING SAID MINERAL-BEARING MATERIAL FROM SAID ZONE, AND ADDING SILICA FLOTATION REAGENTS THERETO BEFORE ANY APPRECIABLE AGITATION HAS DESTROYED THE ACID ACTIVATION OF THE SILICA 